Translating circuits



Patented Dec. 11, 1928.

UNITED sTATEs PATENT OFFICE.

WARREN A. MARRTsoN,` or'EAsT ORANGE, NEW JERSEY, AssIGNoR, BY MEsNE AssIGNMENTs, To WESTERN ELECTRIC COMPANY, TNCORRORATED, A CORPORATION 0F NEW YORK.

TRANSLATI'NG CIRCUITS.

Application led May 6, 1925. Serial No. 28,309.

This invention relates to translating circuits, and is particularly applicable to electrical testing and measuring.

An object of the invention is to simplify the examination and measurement of electrical characteristics.

A related object of the invention is to determine with accuracy and precision the characteristics of electrical circuits and apparatus. I

Another object of the invention is to measure the different current components included in a complex wave. 1

Another object of the invention is to provide a new and improved phase shifter adapted for general use in the electrical arts, whereby any desired change of phase shift can be obtained without circuit interruption.

According toone of its embodiments, the invention provides a simple and elicient arrangement for measuring very small wave components in the presence of relatively large components.

In lexisting current analyzers, for example, considerable diiiculty has been met in measuring such small components due to part of the larger components getting through to the rectifying tubes, in spite of the tuned circuits 1 employed, and causing a steady deflection on the measuring device. This ei'ect may be so great as to completely mask the resonance.

setting for the small componentxor this set# ting may be indicated by only a slight change in the curyature of the curve of deflection versus capacity setting. In such a case it is.

difficult to determine whether ythe smaller component is present. In case the resonance setting for the small components is found,-

this deflection is always added to the steady deflection caused by the larger components. This gives a false reading which is invariably too large, particularly when great sensitivity is desired. p

The difficulties outlined above are vovercome in the present invention which provides means for eliminating the larger components by balancing them against waves of the same frequency but opposite phase. particular feature of the invention resldes 1n the'provision of a novel form of phase shifter, so Combining'a mutualinductance for producing an induced voltage and a resistance for producing an .IR drop, that any desired` change of phase shift can be obtained with- Fig. 1.

The testing system of Fig. 1 may be utilized to measure the distortion or intermodu-J l lation componentsproduced by two or more waves which are simultaneously impressed upon the balanced amplifier 5. It is well known thatI such unwanted components are produced in amplifiers of this type due to the difficulty in securing tubes having identical characteristics and because of the impracticability of exactly balancing the corresponding branches of the divided circuit associated with the tubes.

Alternating current sources O1 and Oz,

which may be themionic oscillators of any well-known type, are conjugately connected to the input of the amplifier 5 bymeans of an alternating current bridge circuit 6 having equal ratio arms; One of the arms of the bridge is connected to the amplifier input'` circuit by means of coupling coils 7 and 8. A balancing network N, simulating the input impedance of the amplifier 5, is connected to the opposite arm of the bridge, thus reventing reaction between the circuits o oscillators O1 and O2.

The'oscillators O1 and O2 are adapted to simultaneously impress waves of different frequencies on the input of amplifier 5. For purposes of illustration, the oscillator O1 may generate a wave of 1,000 cycles frequency, and the oscillator O2 may generate a wave of 10,000 cycles frequency. The voltage output of oscillator O1 may be varied by means of a series resistance 10 and a shunt resistance 11 withoutchanging the impedance of the circuit. Similar series and shunt. resistances 12 and 18, respectively, are included in the output of oscillator O2.

The output circuit of the amplifier 5 is coupled by means of transformer 14 to the input ot a. current analyzer circuit comprismg an amphlier unit and an amphier-rectier unit.

The two-stave am lier unit com risinO thermionic electron discharge tubes 15 and 16 is coupled to the input, of the amplilierrectifier unitby means of transformer 17. The amplifier-rectifier unit com-prises amplifier tubes 18 and 19 and detector tubes 20 and 21. direct current measuring device such as a milliameter` 22 is included in the output circuit of detector tubes 20 and 21.

A tuned circuit 23 is included in the input circuit of the amplifier unit, and asimilar tuned circuit 24 is included in the input circuit of the amplier-rectitier unit. Both tuned circuits may be adjusted to the frequency which it is desired to measure, and 'the rectified output of the current analyzer, indicated upon the measuring device 22, is a unction of vthe alternating current transmitted by the tuned circuits. j

lt will he seen from the above that a wave cf 1,000 cycles frequency generated by the oscillator 01 and a Wave of 10,000 cycles trequency generated by the oscillator 02 are simultaneously impressed upon the input circuit o the amplifier 5. It has also been pointed out above that the Waves of different frequencies tend to react in the amplilier circuit 5, thereby producing cross-talk which, commercial signaling systems, interferes with the eiicient receptionv of signals. This intermodulation may be measured, in accordance with the invention, with a view of determining the distortion produced in the amplitier. v y

When the Wave or" 10,000 cycles frequency is modulated by the Wave of 1,000 cycles frequency in the amplifier 5, sideband frequencies o 9,000 cycles and 11,000 cycles are produced. Hence, the original frequencies of 1,000 cycles and 10,000 cycles, together with the sideband frequencies of 9,000 cycles and 11,000 cycles are impressed through the transformer 14 upon' the current analyzer circuit. ln order to properly determine the intermodulation in the amplifier 5, itis necessary to measure the upper and lower sidebands separately. 1f, therefore, it is, desiredto measure the upper sideband of 11,000 cycles requency, the tuned circuits 23 and 24 are adjusted to resonate at 11,000 cycles. When the tuned circuits are thus adjusted, the 1,000

cycle Wave transmitted through transformer 14 is, for all practical purposes, far enough away in the frequency scale from the 11,000 cycle sideband to be effectively suppressed in the tuned circuits, and hence may be disregarded. Great sensitivity is necessary in making accurate measurements, however, and it is assumed that the 9,000 and 11,000 cycle sidebands are not far enough away from the 10,000 cycle component to be clear of the resonance characteristic of the tuned circuit.

This resonance curve is not `symmetrical about 10,000 cycles, and hence variations in the readings taken at. resonance' tor the upper and lower sidebands are aiected by the presence ot the 10,000 cycle component. Hence, it -is not even possible to make comparative readings of the two sidebands in the presence of the 10,000 cycle component.

l'n order to eliminate the 10,000cycle coinponent which is impressed upon the current analyzer circuit, in accordance with the invention, a portion of the 10,000 cycle current in the output of the oscillator' O2 is balanced against the current in the output of the amplitier 5 on test. rEhe balance is so adjusted that the portion of the 10,000 cycle component which succeeds in passing the tuned circuit 23 is neutralized. Since the lower sideband of 9,000 cycles frequency is eX.- tremely small compared with the 10,000 cycle component, this sideband is eiectively'supf pressed in the tuned circuit 23 and the upper sideband of 11,000 cycles frequency alone 1s amplified and rectified in the current analyzer circuit to give a reading on the measuring device 22.

To accomplish this, a balancing circuit 25 connected to the output of the oscillator G,x is coupled to the input of the current analyzer circuit by means of a three-Winding transformer 26, one Winding of which is connected inthe grid circuit of the tirst stage ampliier tube 15. The third Winding of the transformer V26 is included in the output of a similar balancing circuit 271co`nnected to the output of the oscillator O1. A phase shifter 28, constructed in accordance with the invention,

is included in the balancingcircuit 25, a similar phaseshifter 29 being included in th balancing circuit 27.

The phase of the voltage transmitted through the balancing circuit 25 is so adjusted by means of the phase shifter 28 that the 10,000 cycle component which is transmitted through the balanced amplifier 5 and which succeeds in passing through the tuned circuit 23 is exactly neutralized in the transformer 26. In this Way, only the upper sidef band of 11,000 cycles frequency produced by intermodulation in the balanced amplitier 5 is amplified ,and rectilied in the-current analyzer circuit and caused to actuate the measuring device 22.

The 1,000 cycle component impressed upon the balancing circuit 27-rom the oscillator O1 may likewisebc adjusted by the phase shifter 29 to exactly neutralizein the transformer 26 the 1,000 cycle component which is transmitted through the balanced amplilier 5. As pointed out above, this may not be necessary When measuring the 11,000 cycle sidebandk since, in such case, currents of 1,000 cycles frequencyare readily suppressed in the tuned, circuit 23. In other cases, however, it may be Vnecessary or desirable to i, waves generated by oscillators through any angle, it must bepossible to add i 'two potentials, which themselves differ in phase, in any amount andin either sense. The phase shifter 28 includes a potentiometer resistance 30 and mutual inductances, one of which includes a stationary coil 3l and a movable coil 32, 'and the other of which includes a stationary coil 33 and a movable lcoil 34. The potentiometer contacts 35 are adapted to be rotated simultaneously with movable coils 32 and y34 by means of a common shaft which may be actuated by a gear train 36. Slip rings 37 and 38 associated with the movable coils 32 and 34, respectively, permit the movable coils to be continuously rotated. The principles of operation of the phase lrifter will be described in connection with In Fig. F2, the coils a and b are inductometer coils, one of which can be rotated to vary the mutual inductance between them. The coil b and the resistancey or potentiometer element; o are included in the input circuit of the phase shifter while the coil a and a part or all of the resistance c, according to the amount of phase shift desired, are in the output circuit. The coil a and the contacts of the potentiometer resistance are mounted on a common rotating shaft so that both the -inductance and resistance can be varied simultaneously.

The current' z in the input circuit is equal to I` sin at and can be assumed constant for4 purposes of this discussion. The voltage cl is the voltage across the inductance a and is equal toy E1 cos wt, while e2 is the voltage across the portion ofthe resistance c included in the output circuitand is equal to E2 sin et. Thus it follows that-y e which is the total output voltage and the vector sum of e1 and e2 is lequal to E sin (mt-ht).

Since it is advisable for most purposes to have a constant amplitude of lthe output voltage regardless of phase, the distribution ofthe resistance of the potentiometer may lbe so chosen that the amplitude of the sum of el+e2 is equal to a constant. That is,the elements of the phase shifter may be so designed that for any angular displacement of the control shaft, and consequently the inductometer coils, the output voltage may 'be represented by E E21 +2 =I1/R2+w2M2 where E is the absolute or root mean square val-ue of thisfvoltage.

Since the impedance of the output circuit is high, there will be practically no current flowing therein, and the following relations approximately hold g -and Where M is the mutual inductance between the inductometer coils, R the resist-ance between the contacts on the potentiometer and c) lS 21rf. d

If 0 represents the angle between the inductometer coils, then the mutual inductance M'variesas thecosine of the angle 0; and 'f wherel mo is the maximuminductance,

` 4 M :Mo cos 6. Substituting for M in equation 1 E I\/R2 wZMozcosG (2) When the resistance contacts are in such position that R=O, the total output voltage is provided by the coil a so that E=IM0 Now substituting for E in Equation 2 there results:

Given a definite value of Mo and f the distribution of resistance caLn be plotted as a function of @by substituting in the final equation. This gives the -basis for the potentiometer construction which provides a constant output volt-age regardless of phase. lVhen the potentiometer resistance 30 of the phase shifter of Fig. 1 is constructed in this manner, the actuating element of the resistance and the movable inductometercoils 32 and 34 may be proportionately displaced tosimultaneously vary the mutual inductance and the resistance of the circuit in order to maintain the amplitude of the sum of the two potentials constant. ,7 o z The phase shifter of Fig. l may also be continuously rotated by suitable power apparatus associated with the gear train 36 to modify at will the frequency of the current supplied by afrequency standard such as 'the oscillator O2. As each revolutionof the comf mon control shaft shifts the phase of the wave impressed upon the circuit 25 by 360 degrees, rotation at the rate of one revolution per second will add or subtract one cycle from the frequency of such wave according to the direction of rotation.

' Fig. 3 shows a modification of the phase shifter or" Fig. 1 employing a diierent construction ot the potentiometer resistance. lnductometer coils 40 and 4l are mounted on the same controlling shaft as the resistance contacts 42. The distribution of resistance in the potentiometer 43 is theoretically identical to that of the potentiometer resistance ot the phase shifter 28.

-While definite frequencies and specific circuit arrangements have been described for the purpose of illustrating the various features of the invention, it is to be understood that deviations may be made therefrom-without departing from the spirit and scope of the invention as defined in the following claims.

'What is claimed is:

'1. phase shifter comprising an incoming circuit, an outgoing circuit, a plurality of fixed and rotatable coils, a resistance element, said coils and resistance being conductively connected to said incoming and outgoing circuits, a plurality of rotatable resist? ance contacts engaging said elements and means for rotatingr said resistance contacts simultaneously with said rotatable coils whereby a shiftin phase can be obtained between the voltages in said incoming and outgoing circuits.

2. A phase shifter comprising a pair of fixed coils, a rotatable coil inductively coupled with each of said fixed coils, a potentiometer resistance element, a pair of resistance contacts conductively connecting said potentiometer element to said rotatable coils, and means for rotating said contacts simultaneously with said rotatable coils or obtaining any desired shirt in phase in currents passing through said coils Aand said potentiometer element.

3. A phase shifter comprising a plurality of iixed and rotatable coils, a resistance element, a plurality of rotatable resistance contacts engaging said element means for rotating said contacts simultaneously with said coils, and a plurality o slip rings and contacts associated therewith for maintaining a circuit between said coils and said resistance element. Y

4. A phase shifter comprising a pair of fixed coils, a rotatable coil associated with each of said fixed coils, resistance contacts rotatable with said rotatable coils, and a potentiometer resistance in circuit with said coils through said contacts, the relationship between the mutual inductance ot said coils and the resistance of said potentiometer prof viding a constant output voltage with any shift in the phase angle thereof.v

5. A phase shifter comprising a pair of ixed coils, a rotatable coil inductively coupled, with eaclrof said fixed coils, resistance contacts rotatable with said rotatable coils, a potentiometei` resistance conductively connected to said coils through said contacts, and means for rotating said coils simultaneously with said contacts, the resistance being so distributed on said potentiometer that the value of the resistance between said contacts is a function of the angle between said hired and rotatable coils.

G. A phase shifter comprising a mutual inductance device having fixed and movable coils for producing an induced voltage, a resistance conductively connected to said fixed and movable coils for producing an IR drop, means for electively varying the amount of said resistance in circuit with said movable coils orobtaining any change of phase shift in currents through said coils and said resistance while maintaining a constant output voltage.

'i'. A phase shifter comprising an incoming line, an outgoing line, a pair of xed coils, a rotatable coil inductively coupled with each of said fixed coils, a potentiometer resistance element, a pair of resistance contacts connecting said element to said rotatable coils, a pair of slip rings, a pair of slip ring contacts connecting said slip rings to said rotatable coils and means comprising a gear train for rotating said slip ring contacts, resistance contacts and rotatable coils, simultaneously for controlling the phase shift between said incoming and outgoing lines.

8. A phase shifting device comprising a pair of fixed coils, a rotatable coil inductively coupled with each of said fixed coils,

a potentiometer, a pair of resistance contacts conductively connecting said potentiometer to said rotatable coils and means ormoving said contacts simultaneously and cont-inuously with said rotatable coils for obtaining any ydesired change in frequency in currents passing through said coils and said potentiometer.

9. A phase shifting device comprising an incoming line and an outgoing line, a pair of hired coils, a rotatable coil inductively coupled with each of said xed coils, apotentiometer resistance element, resistance contacts connecting said element to said rotatable coils, a pair of slip rings, a pair of slippering contacts connecting said slip rings to said rotatable coils, and means comprising a gear ltrain for rotating said coils, resistance and slip ring contacts simultaneously and continuously for controlling the diierence in frequency between the voltages in said incoming and outgoing lines.

10. A phase shifting device comprising a pair of fixed coils, a rotatable coil associated with each of said fixed coils, resistance contacts movable simultaneously and continuously with said rotatable coils, and a potentiometer resistance connected to said coils through said contacts providing a constant output voltage with any change o frequency between said outgoing voltage and an incoming voltage.

l1. Ina phase shifting device comprising an incoming circuit and an outgoing circuit, a plurality of fixed and rotatable coils, a resistance element, a plurality of movable resistance contacts engaging said element, said coils, Contacts and resistance element conductively associated with said incoming and outgoing circuits, and means for moving said resist-ance contacts and rotatable coils simultaneously and continuously whereby a difference in frequency can be obtained and maintained between the voltages in said in coming and outgoing circuits.

In witness whereof, I hereunto subscribe my name this 5th day of May A. D., 1925.

WARREN A. MARRISON. 

